Field of Invention
The present invention relates to systems and methods to enable medical device delivery into a patient's body, more particularly to systems and methods to protect tissue from injury during manipulation or after implantation of medical devices.
Description of Related Art
Devices such as catheters and leads have long been used in medicine to position within various organs or cavities in the body. Some of these devices cause trauma to the adjacent tissue with which they make contact due to the force with which they are advanced or placed, causing complications and poor outcomes. Perforation of organs by these catheters and probes causes significant morbidity and mortality. Soft material positioned at catheter tips is sometimes used to minimize tissue disruption by the tips of devices. These tips have improved safety, but they provide little spring force or distribution of the loads applied by catheter advancement. In addition, there are cases in which the catheter tips are intentionally applied against tissue, but there is little to no user feedback regarding the amount of applied force at the tip or the proximity of the tip to the tissue with which it is in contact. Additionally, the tips are non-conductive and so are not useful for applications such as cardiac rhythm management or tissue signal recordings.
For example cardiac pacemaker and defibrillator leads are positioned on a temporary or long-term basis in patients with heart disease. The contraction of the heart is controlled by specialized tissue that conducts an electrical wave across the heart muscle. That electrical wave controls and coordinates heart muscle contraction. In certain medical conditions, the conduction system of the heart is abnormal, leading to slow or abnormal heart rhythm. Physicians often need to insert catheters into the heart to correct the problem. These catheters have one or more electrical conductors that are connected to a device that generates rhythmic electrical current to control, or pace, the heart contractions. One conductor is usually positioned at the distal tip of the catheter. The catheter is typically inserted into a heart chamber through a blood vessel. The tip of the catheter is usually pushed up against the inside of the heart chamber to place the electrical conductor is contact with the heart tissue. A current is transmitted through the catheter to the heart muscle, pacing the muscle to contract.
One problem with these pacemaker catheters or leads is that they can perforate the heart tissue. To provide electrical contact to the heart muscle, the catheter or lead must be pushed to provide some level of force against the heart muscle. Contraction of the heart muscle against the catheter or lead may cause the catheter or lead to erode through or perforate the muscle wall. Perforation leads to leakage of blood from the heart to the pericardial sac that surrounds the heart. When the pericardial sac fills with blood, the heart is compressed from the outside and cannot fill with blood. This condition is called cardiac tamponade, which untreated often leads to death. Perforation occurs because the force applied to the tip of the catheter pushes the catheter into the muscle, which in places (such as the right ventricle, the left or right atrium, or the apex of the left ventricle) can be quite thin. Similar erosion may occur when catheters or leads are in contact with other organs. Motion or simple continued force may cause erosion or burrowing of the catheter or lead.
These procedures result in complications such as the aforementioned cardiac perforation in up to 2% of the procedures. Several methods have been used in the past to reduce the possibility of tissue trauma. One embodiment includes combining a catheter with an inflatable balloon tip while others use softer catheter tip materials that are less likely to cause trauma. These have their own limitations related to suboptimal stability and potential migration. Migration of a pacer lead, or loss of capture, results in an immediate inability to pace the heart muscle which can be deadly in a patient that requires pacing to ensure adequate rhythm.
Additional difficulties in positioning the catheter include placing it at the exact place needed or preventing its migration due to the poor ability to secure them at the area of need. There are designs and methods that incorporate deflectable catheters to help with positioning and micro screw-in catheters for securing the catheters into the tissue that have been used in various embodiments.
However, these existing methods have various limitations including the risk of poor contact at the required site, risk of trauma leading to organ perforation, migration away from area of implant or being flimsy or difficult to maneuver.
Determination of the position of the catheter or lead relative to the organ is also important in providing proper, safe apposition of the tip to the organ, in particular the completeness of contact and determination of the proper amount of tip pressure. Location, position and orientation of catheters can be determined by a combination of tactile feedback and visual imaging based on fluoroscopy, which require substantial physician judgment based on experience. Fluoroscopic images provide a general sense of location, but verification of the catheter location relative to internal vessel or cavity margins require injections of contrast media to define a two-dimensional picture of the target space. During a complex procedure in which a catheter is intended to be placed against a target site, a number of contrast injections may be necessary to continually verify that positioning remains adequate. These contrast injections can add to patient risk by increasing the demand on the kidneys of the patient, particularly in patients that are already at risk of kidney failure. In extreme cases, this increased load can result in a condition known as contrast induced nephropathy.
Another catheter example is one used in the heart to record the local intracardiac electrical activity (intracardiac electrocardiogram). Similarly, therapeutic catheters used to delivery energy (such as radiofrequency energy to alter cardiac tissue), alter cardiac temperature (such as cryoablation catheters), or image cardiac tissue (such as ultrasound catheters) require precise placement and inappropriate use can perforate the heart muscle. There are also catheters used to procure tissue samples called bioptomes or biopsy forceps. These catheters are used to navigate to a selected target area and cut a small piece of tissue from the target site for examination. During this tissue extraction, excessive force on the catheter during advancement or actuation can also result in perforation. Other catheters are used to provide for stabilization and positioning of puncture needles to facilitate the crossing of membranous tissue such as the intra-atrial septum.
Additionally, there are systems that are used to deliver contrast or therapeutic agents to the vasculature, the heart or another target site in the body that do not have a mechanism to stabilize the system or protect the tissue from damage. Straight guide catheters and pigtail catheters are often used for contrast injection at a location such as the left atrium. In certain locations, the left atrial wall can be as thin as 0.5 mm between the pectinate muscles which would make it susceptible to perforation or damage during a high-velocity contrast injection if the catheter orifice is too close to the atrial wall when the injection is performed. Similarly, needles are often used to inject stem cells into the wall of the left ventricle with little control over catheter tip position, relying on physician skill to stabilize the catheter tip position during the procedure.
While catheterization is often performed in order to access the vasculature and the cardiac anatomy, it is understood that similar devices are used in a number of other locations within the body. The use of and risks associated with the existing technology as described above certainly apply to these other areas as well, including but not limited to bladder examinations and biopsy, colonoscopy procedures and biopsy, and general endoscopic surgical procedures.
A device that can provide improved tactile or visual feedback related to system proximity to target tissues, as well as catheter tip stabilization and approximation of an expandable surface to distribute the tip apposition force imparted by the catheter across a greater surface area in order to reduce focal pressure would ultimately result in safer system use, reduced patient risk and better patient outcomes.